This study reports the role of pressure (0.1-4.0 MPa) and temperature (600- 900 degrees C) in flash pyrolysis of palm kernel shell (PKS). The main objective was to study the extent to which pressure affects the mechanism of pyrolysis reactions to enhance the selective production of target products. Higher pressures and temperatures selectively promoted the generation of polycyclic aromatic hydrocarbons (PAHs) and H-2 gas. Bio-oil samples generated at lower temperatures and pressures were mainly composed of phenolics. Increasing the pressure and temperature favored the selective formation of phenanthrene, fluoranthene, pyrene, fluoranthene, and fluorene, which reached 96.17 area %. Elevated temperatures and pressures enhanced hydrogen transfer into a light gaseous phase. The yield of H-2 peaked at 40.82 g of H-2/kg of PKS at 900 degrees C and 2.0 MPa. The results obtained in this study implied that the pyrolysis of biomass at elevated pressures can be an effective method for polygeneration of hydrogen gas and PAHs as chemical feedstocks.